The present invention relates to a seat belt locking device, particularly to a seat belt locking device which is installed in a seat belt system of a vehicle together with an emergency lock retractor.
The seat belt system for restraining the occupant of a vehicle is generally provided with an emergency lock retractor by which the seat belt is wound upon or withdrawn according as the physique and the motion of the occupant and by which the seat belt is prevented from being extended at an emergency time such as upon impact of the vehicle.
In a locking mechanism of the lock retractor of this type, the seat belt is usually wound upon a reel which is rotatably supported by the emergency lock retractor and at an emergency time, the seat belt is prevented from being withdrawn from the reel by locking the rotation of the reel by means of a ratchet gear.
Various means have been adopted for operating the ratchet gear at an emergency time such as upon a vehicle impact. And by any of the above described means, the rotation of the reel upon which the seat belt is wound is stopped.
Therefore, when high load of the occupant is applied to the seat belt at an emergency time such as upon a vehicle impact, the seat belt portion which is wound upon the locked reel is tightened and extended out of the reel by a length corresponding to the tightened seat belt portion. And also the seat belt itself stretches due to the high load so that the occupant is in danger of moving forward largely.
In order to prevent the seat belt from being extended out of the retractor after the rotation of the reel is stopped, a locking device which locks the seat belt itself when the reel of the retractor is locked has been conventionally provided in the emergency lock retractor.
One example of the above described locking device locks the seat belt by catching the seat belt between rollers or between a roller and a plate. And in most cases, knurling is formed in the belt catching surfaces of the roller and the like in order to increase the friction force of the belt catching portion.
As a result, according to one example of the conventional locking device, the belt catching force becomes large but the seat belt becomes easy to be broken.
When the seat belt is broken, the occupant is utterly released from the restraint of the seat belt so that the seat belt cannot fulfil its function.
Accordingly, one object of the present invention is to provide a seat belt locking device which surely locks the seat belt itself on the side that the seat belt is withdrawn from the emergency lock retractor when the reel of the emergency lock retractor is locked.
Another object of the present invention is to provide a seat belt locking device having a means which prevents the seat belt from being broken.